1. Field of the Invention
The invention relates to a method for reducing the contact resistance, and especially is related to a method that effectively removes the residuals and oxides by inducing etch process.
2. Description of the Prior Art
For a semiconductor product, a conductive structure is usually formed over another conductive structure to form a complete conductive or a complete device. For example, for the thin film transistor (TFT), a conductor layer, such as polysilicon layer or amorphous layer, is etched to form the source/drain of the TFT, and then a dielectric layer is formed over a patterned conductor layer. Next, some openings are formed in the dielectric layer to expose partial patterned conductor layer, and then a patterned metal is formed on the dielectric layer and in the openings to form the required conductive line.
Clearly, the contact resistance between some adjacent structures is a portion of the resistance of the complete semiconductor device. Moreover, each semiconductor structure is made of conductive material with low resistance, which means their resistance is predictable and controllable, and the contact resistance is induced by the practical fabricating process, which is hardly predicted and controlled. Hence, reduction of the contact resistance is an important problem. Especially, a conductive structure is usually formed by etching a deposited conductive layer into a required pattern, but the etching process usually produces residuals and oxides on the etched surface such that both the resistance and capacitance on the etched surface are increased. Hence, prevention of the effect of the residuals and oxides is the key to reduce the contact resistance.
Regarding the problem, the prior art has the following solution: using the helium gas plasma to treat the patterned surface to remove residuals and oxides, while the etching process is just finished; using both the helium gas plasma and hydrogen gas plasma to treat the patterned surface to remove residuals and oxides while the etching process is just finished; or using the cleaning process, such as wet solution cleaning process and gas cleaning process, to treat the patterned surface for removing residuals and oxides before any sequential process is performed. However, according to the experimental datas, all prior art only can reduce the number of both residuals and oxides but can not let the number of both residuals and oxides be reduced to be negligible, especially the oxides on the patterned surface cannot be removed effectively. Therefore, the effect of contact resistance between adjacent conductive structures is still negligible.
Accordingly, it is desired to develop a new technology to effective remove both residuals and oxides on the patterned surface. Moreover, to reduce the cost and difficulty, it is important to develop a new technology which is compatible with the conventional fabrication of semiconductor product.